Wesnoth players who wish to improve their battle results can learn from Napoleon.

[Napoleon held that, in] order to concentrate superior combat strength in one place, economy of force must be exercised in other places. Economy of force requires the acceptance of prudent risks in selected areas to achieve superiority at the point of decision. One account has it that Napoleon allowed a subordinate to draw up a plan for the disposition of his troops. Not knowing what the Emperor wanted, the subordinate distributed the forces equally in neat little groups along the border. On seeing it Napoleon remarked, "Very pretty, but what do you expect them to do? Collect customs duties?" (Source: http://www.napolun.com/mirror/web2.airm ... actics.htm.)

Not a military officer, I have commanded no real troops in battle. Nevertheless, in The Battle for Wesnoth, I can report this: experience tends to confirm Napoleon's advice. In single-player campaign mode at hard difficulty, Napoleon's advice brings victory when other approaches risk defeat.

This article explains and explores Napoleon's principle of the concentration of forces as manifested in The Battle for Wesnoth.

The article has nine sections. It begins with an overview of opposites: dispersion and concentration.

I. DISPERSION AND CONCENTRATION

Until the foe's main body draws near, one can disperse forces at discretion. One can seize villages, left, center and right. One can hunt, contain or harass the foe's advance scouts. One can, and should, pursue preparatory objectives as appropriate.

However, when the foe's main body draws near, if the foe concentrates forces faster than you, then the foe will usually win. If the foe concentrates while you do not, then you will normally lose the scenario.

What is concentration? Concentration, as here defined, is the massive assembly of coordinated forces, ready to fight, prepared to violently achieve an objective of battle via the attempted disruption or destruction of enemy forces opposing. Concentration implies several or many units. No unit can concentrate alone.

Dispersion is the opposite. It is the scattering of coordinated forces, whether to avoid presenting a massed target to a superior foe or to achieve several battle objectives simultaneously against weak opposition.

Many operational plans are possible at Wesnoth. Most good operational plans feature strong concentration at the point of decision. At hard difficulty, failure to concentrate is normally an irremediable flaw.

Here is an example from the Heir to the Throne campaign:

Spoiler:

In scenario 9, The Valley of Death, at hard difficulty, a plan one can adopt is to attack and destroy the southwestern foe and his army early, before the armies of his two allies can arrive. This is a classic Napoleonic maneuver, but beware: if you would execute this maneuver, then you should commit sufficient forces to it—the more forces, the better. You might send a one- or two-unit assassination squad northwest and another such assassination squad southeast to flank and surprise enemy chieftains from the rear on the morning of the battle's second day, but other secondary objectives are probably insufficiently profitable to pursue. Other secondary objectives are insufficiently profitable to justify the eventual loss of concentration they imply. For example:

It is tempting to leave a sacrificial rearguard in the castle in the center of the map to delay the approach of the two armies.

It is tempting to send a scout or two northeastward to capture villages.

These are costly temptations. At The Valley of Death as in many other scenarios, the wise general will resist such temptations. Concentration is not to be so cheaply compromised.

Admittedly, in some scenarios, auxiliary objectives are sufficiently profitable that one will reluctantly devote minimal forces to them (especially, one will sometimes dispatch a scout to capture distant villages). There are also scenarios at which a central geographical obstacle requires an anxious division of forces, left and right. However, in the scenario of the example and in many others, such tactics are defective because they fail to concentrate one's forces at the point of decision.

Surprisingly often at hard difficulty, a single extra unit decides the battle. Do not let that unit be caught away from the main battleground during the battle's critical turn!

II. CONCENTRATION TACTICS

To concentrate forces does not mean to cram all one's units into the densest possible circle. On the contrary, your units will need some room to maneuver. Indeed, when I have many units crowded along a narrow front, two or three ranks deep, I will usually try to leave 30 to 35 percent empty space in the second and third ranks for room to maneuver. Also, if practicable, far from disposing my forces within a dense circle, I will usually extend my front line far enough to the left and right (but not too far) to prevent the enemy from flanking my line to kill my wounded units.

However, to concentrate forces does mean the following.

One's slowest, rearmost heavy-hitting units must stand close enough to enemy forces that they can begin the turn by moving forward to immediately destroy the enemy's most valuable front-line forces.

One's other heavy hitters must stand even closer (or be faster) for, once the first wave has degraded or destroyed the enemy front, a second wave should during the same turn immediately advance through to degrade or destroy vulnerable enemy forces to the rear. The second wave should only take care not to advance so far that it risks its own destruction during the foe's coming turn. In other words, the second wave should only take care not to advance so far that it inadvertently forms its own, separate, miniature battle group with inferior concentration relative to the proximate foe. Otherwise, the second wave should advance, degrade and destroy within the foe's rear ranks; for, to the extent to which the second wave achieves this, the foe shall during his coming turn lack effective forces with which to respond.

To end the turn, disposable units and other screening forces need already to be at hand to move into position to shield spellcasters and other vulnerable units of the second wave in forward positions.

One, two, three: destroy with the first wave; advance with the second wave; shield with screeners. Adequately to coordinate these three during a single turn is seldom possible unless you have concentrated sufficient forces before the turn begins.

Therefore, concentrate.

During the critical turn, if you run short of forces at the point of decision—if your concentration proves inadequate—then you will probably lose the scenario. Surprisingly often at hard difficulty, a single extra unit decides the battle. At the crucial moment, you do not want that unit to be off wandering on some irrelevant side mission from which the unit is unable to impact the main battleground in time. Forlornly will such a unit arrive, alas, too late; as a fallen leaf driven by the winter wind across a bleak, barren field, such a unit is but the straggling herald of needless defeat.

III. RELATIVE CONCENTRATION

Concentration of forces is important but concentration of forces is also relative. You shall have achieved potentially effective concentration whenever and wherever your concentration is momentarily, locally superior to the foe's.

According to the principle of relative concentration, a good general may seek briefly to delay his great stroke until his forces have assembled unless the foe's forces are assembling faster.

Often therefore, relative concentration means striking without delay.

In other words, if waiting another turn will strengthen you but will strengthen the foe more, then you probably should not wait.

IV. CONCENTRATION AND THE TIME OF DAY

In The Battle for Wesnoth as you know, the time of day is a force multiplier. In other words, the time of day is a concentration multiplier. Therefore, the best Wesnothian general will have contrived, a few turns in advance, to schedule the critical turn to occur during favorable daylight.

V. QUICK-UNIT TACTICS

A perplexing question that often arises regards whether to position one's quick units in the center or on the flanks. My experience suggests no one right answer to this question. However, as a default rule, if concrete circumstances do not recommend otherwise, I have usually found it more profitable to position units with the quick trait in the center. That way, if an unexpected need arises on a flank, I can pull the quick unit out of the center and transfer it immediately to the active flank.

Of course, it can be even better to pull a quick unit off a flank and transfer it all the way to the opposite flank. I lack a firm doctrine on this point, nor do I know what Napoleon would advise; but in my experience at Wesnoth even a quick unit is usually not fast enough to satisfactorily maneuver from flank to opposite flank during the battle's critical turn. Reason: it may be insufficient for the unit merely to reach the opposite flank; but rather to maneuver a bit once the unit has got there. No, on average, unless the center is a salient or other exposed position requiring a resilient unit, it seems better to have positioned the quick units in the center.

VI. ACCEPTABLE BATTLE LOSSES

To win often at hard difficulty, you will have to lose a few non-loyal units. Exposure along a front of battle is a risk. To some units, this risk will prove fatal.

To which units will the risk prove fatal? Usually, you won't know which. The dice will decide. You can improve your odds by exposing healthy units while wounded units heal, but you cannot consistently win without losing units at all.

And here is the unpleasant, yet interesting thing. At hard difficulty, it is not only the level-one units that you will lose, but also sometimes the level-two. Easier scenarios are often possible to complete without level-two losses; but if you can complete a harder scenario with the loss of no more than one level-two unit, then you should probably count that a success. (If you lose two level twos or if you lose a level three, that's not so good. That happens, too; but if it happens often, then the campaign will admittedly be hard to complete. You want a balance: sufficient risk to achieve necessary battle results now; sufficient preservation of own forces to fight future battles, too.)

Of course, because The Battle for Wesnoth is a game, you can always restart a scenario to recover an otherwise lost level-two unit; but this article assumes that you want to win the scenario on the present attempt, not merely to win on some future attempt during which lucky dice happen to favor you. If you want to win the scenario on the present attempt, then you must accept some losses in battle.

What ratio of losses in battle can one accept? Answer: it depends on the scenario, but roughly, at hard difficulty, about 1:8, one to eight. If your foes lose approximately eight units for every one you lose, then you are probably doing all right.

As far as I can tell by reading the forum over the years, trying to win battles with zero battle losses seems to be not an uncommon error among Wesnoth beginners. Trying to win battles with zero battle losses is also a fairly sure way to lose battles at hard difficulty. Zero battle losses is not aggressive enough. Judicious but robust aggression, leveraging a superior concentration of forces, wins battles while preserving most of your forces precisely by destroying the foe's army before it can assemble to destroy yours.

You just cannot do that without the loss of a few units. If you could, then how interesting a game would The Battle for Wesnoth be? A hammer's heavy fall will jar the arm that drives the stroke, as it were, even as the hammer's fall shatters the thing it strikes.

Regarding the inevitable level-two losses, that is why you need to be mentoring level-one units, helping them to gain experience to rise to level two. You will need some rising level twos to replace the level twos you lose. And observe: the harder the difficulty level, the more foes to destroy, the more experience to earn, the more units to promote. At hard difficulty, if you're surviving at all, then your recall list will probably not be suffering a severe shortage of level-two units.

VII. EXAMPLE

A replay at hard difficulty is attached. It is from the same campaign as the above spoiler, but an earlier scenario. In the replay, victory is achieved despite several bad die rolls early (late dice were better). Only a Napoleonic concentration of forces retrieves hope of victory from the early bad dice.

Spoiler:

The scenario is number 8, The Princess of Wesnoth.

VIII. EXCEPTION: THERMOPYLAE

In real history, 480 B.C., bottlenecked terrain at the Battle of Thermopylae constricted the front of battle so straitly that the Persians, who had otherwise concentrated superior forces against the Greeks, lost the battle, anyway. Such a situation affords a rare exception to the principle of concentration of forces. At Wesnoth, where sufficiently hard-to-pass terrain secures both flanks, thus preventing the foe from applying the full weight of his forces at once, there one need not concentrate, but need only bring sufficient forces to hold the gap. At Wesnoth as in history, however, such a situation does not often arise, for even one insecure flank defeats the tactic of Thermopylae.

IX. CONCLUDING REMARKS

I cannot say how realistic Napoleon would find The Battle for Wesnoth to be. However, I can say that Napoleon's advice seems to bring victory in the game. The concentration of forces is not the sole principle of warfare. There are others. One will sometimes need to spare a few units toward a secondary objective.

However, the wise general begrudges every unit spared. He concentrates his forces, rather. He concentrates his forces at the point of decision, where alone he can destroy the foe's ability to resist.

(This article has been updated. Its acceptable-loss ratio has been relaxed from 1:10 to 1:8 and its empty-space fraction has been increased to as much as 35 percent. See also sections X, XI and XII, posted below as a reply; and sections XIII and XIV, posted below as another reply.)

oaq wrote:trying to win battles with zero battle losses seems to be not an uncommon error among Wesnoth beginners

I was certainly one of those beginners. The first tips that beginners see are likely to be the hints on the title screen, maybe some hints should be added about the necessity of disposable units. And yes, that sounds like I'm volunteering to write them.

Thanks for the essay and replay, it was informative both on the use of troops, and the use of villages as lures.

@octalot, your early comment is acknowledged and appreciated. Such a battle tip as you suggest would seem edifying to me.

Also, tangentially, your early comment has jarred loose a stray thought or two from my mind, adding to the article tenth, eleventh and twelfth sections as follows. Section XII responds to your mention of lures.

X. THE TIMING OF CONCENTRATION AND OF RECRUITMENT/RECALL

Experienced Wesnothian commanders realize that it can be imprudent to recruit and/or recall forces too early. A battle's main engagement seldom occurs during turn 1, 2 or 3. Concentration is useless, even counterproductive, if it happens before a partially massed foe has advanced to present a suitable target to strike.

Experienced Wesnothian commanders can minimize the early recruitment/recall of non-loyal units to gain time to capture villages to support other units later to be introduced.

Even if recruitment/recall is not delayed, a scenario's early turns can be, and usually are, a time for dispersed forces simultaneously to achieve preparatory objectives in areas distant from the eventual main battleground. However, beware: a commander must judge from the scenario's start whether a given preparatory objective would take too long to achieve, for a preparatory objective whose pursuit frustrates eventual concentration at the point of decision is seldom worth pursuing. Indeed, if a preparatory objective fails to prepare for the eventual moment of decision, then what useful, alternate goal does the commander believe that the preparatory objective might promote? Victory at the point of decision alone renders all other goals achievable.

Spoiler:

In the above replay of The Princess of Wesnoth, observe that Ronry and his friends are not provoked to emerge from their mine until the princess's first three assault waves have been met, concentrated against, and largely destroyed.

XI. CONCENTRATION VERSUS THE EFFECTIVE USE OF TERRAIN

The principle of concentration can be stretched, even moderately abused, to take advantage of favorable terrain like a river's bank. Even so, however, the wise general will usually avoid stretching the principle too far.

If favorable terrain lies so distant that forces stationed there cannot be withdrawn to impact the main battleground, at the latest, on the second turn of decision, then the favorable terrain in question probably lies too distant to be worth occupying.

Naturally, favorable terrain within the main battleground itself, even if merely on the battleground's flanks, is more valuable.

Sometimes, the foe will enjoy the initiative to choose where the point of decision will occur. For example, where a river presents a concave shape to the foe and terrain favorable to the foe lies on the foe's side of the river, you will be unable to dictate to the foe where he should strike. At such times, to occupy not-too-distant favorable terrain while one waits for the foe to commit may be the best one can do.

XII. THE VILLAGE AS A LURE

The AI likes villages. Since the control of villages is usually necessary to win a scenario, the AI is right to like villages; but, realizing that the AI likes villages, you can use the villages the AI likes to your advantage. You can use the villages the AI likes as lures.

Where the AI sends a unit to capture a flanking village, you can send minor, locally superior forces to destroy the unit and recapture the village. If your minor forces, or at least some of them, can return to the main battleground in time for the moment of decision, then to use such a village as an early lure can be an effective operational plan.

Especially fun, if you are desperate and the scenario's time is running out, is to lure the enemy's chieftain to occupy a village in which the chieftain can be destroyed. Counterintuitively, you can sometimes lure a chieftain by placing a unit of your own immediately next to the village, where the chieftain can personally strike the unit and then heal 8 points to begin the next turn. AI chieftains like that. Unfortunately for the AI, you can trap the chieftain in the village, making the village itself the point of decision, while the chieftain's last-recruited unit languishes, useless, back in the chieftain's camp. Such a lure may not greatly improve your own concentration but it can tempt the foe to the critical error of voluntarily disrupting his own concentration.

The last is a tactic of desperation, meant to salvage an otherwise lost scenario; but the earlier mentioned lures, on the flanks, represent sound operational policy insofar as they secure villages while destroying enemy forces early—enemy forces which therefore later, when the moment of decision occurs, remain unavailable to the foe to concentrate.

A recent discussion in another thread has brought to mind another way to characterize the concentration of forces, so let's add sections XIII and XIV to the article, as follows.

XIII. A QUANTIFIABLE METRIC

The first unit brought to the main battleground is worth 1.0 unit.

The second unit brought to the main battleground is probably worth about 1.5 units. Reason: if the first unit wounds an enemy, then the second might slay the enemy, which deprives the enemy of the chance to strike back next turn.

The third unit brought to the main battleground is probably worth about 2.0 units.

The fourth unit brought to the main battleground is probably worth about 2.5 units.

The fifth unit brought to the main battleground is probably worth about 3.0 units.

The sixth unit brought to the main battleground is probably worth about 3.4 units.

The seventh unit brought to the main battleground is probably worth about 3.7 units.

The eighth unit brought to the main battleground is probably worth about 4.0 units.

The ninth and each subsequent unit brought to the main battleground are probably worth about 4.0 units each.

On the other hand, admittedly, if the main battleground grows so crowded that extra units cannot fit, or if it spreads so wide that extra units cannot quickly redeploy to needed positions, or if the commander lacks the skill to coordinate units in their respective echelons, or if the enemy commander has the skill to frustrate the coordination of units, or if the enemy has sufficient reserves to deny penetration by plugging gaps in his own line, then extra units begin to have less value. However, the aforementioned nine are a lot of units. Usually, overcrowding and such are not the problem.

If you are more mathematically inclined: to a first approximation, relative striking power goes as the square of the number of concentrated units. Reason: if I have twice as many as you, then I can inflict twice the damage, and I can concentrate that double damage on a target half the size; whereas you can inflict half the damage on a target twice the size.

This is why just one extra striking unit, brought in time to a battle's decision site, so often turns the battle. Because it's not just one unit. It's one unit, multiplied by the force of all concentrated compatriots. The one extra unit can prove to be worth as much as 4.0 units on the margin.

Think of four policemen. Coordinating, trained, four policemen can subdue and arrest even the strongest of strong men. The four are as more than four, because of concentration of forces.

I have not tested the suggested numbers. Undoubtedly, the numbers are rough, but the principle holds as far as I know.

XIV. ACTION AWAY FROM THE POINT OF DECISION

A beginner might mistake the article to imply that action away from the point of decision were of minor importance in The Battle for Wesnoth, but this is actually the opposite of the truth, as Napoleon himself would likely have insisted. Let me explain.

One can bring relatively superior forces to the point of decision, ready to fight, only by robust, balanced, extended preliminary action—action designed, on the one hand, to augment, time and concentrate one's own forces and, on the other hand, to suppress, distract and disperse the enemy's forces. It is not that the rest of the scenario is unimportant, but only that the rest of the scenario may become unimportant if the commander forgets what the rest of the scenario is actually for—if the commander forgets that the rest of the scenario is to establish preconditions for triumph at the point of decision.

Then, when the point of decision is at last reached, to the extent to which preparation has succeeded, sharp tactics during a single turn, or perhaps during two turns, can decide the issue.

So the game brings a balance, does it not? It brings extended, various preparation on the one hand, and—in many scenarios—a sharp summit of decision on the other. A key to victory is to judge just when to abandon further preparation, converging toward the one point at which the enemy can be broken and the battle can be won.

One addendum, which relates to your Thermopylae example. Concentration of forces do not only relate to numbers but to capability as well. Replacing a level 1 unit with a level 2 unit in the battleline is also a form of concentration, and a unit with leadership acts as a force multiplier for several units. If you have several level 2 units, you have the choice of either using them together or interspersed with level 1 units. The difference between no unit and a level 1 unit on a hex is much greater than the difference between a level 1 and a level 2 unit, so there is less concentration penalty to splitting up the level 2 units.

There is also such a thing as too much concentration, on both the macro and the micro level.

On the micro level, it's most apparent in fighting a severely wounded and pinned unit. If you have say a 3 HP orc that's ZoC, and the only unit that can attack it is an archer that have other viable targets, it might be better to attack some other orc that might receive far more damage. (Of course, local tactical considerations will be the deciding factor here.)

On the macro level, with too many units in too narrow an area means that it's hard to rotate wounded units back and bring the heavy hitters to "safe" hexes to attack from, or that a large part of your army can't fight on a given turn. Being stuck behind your own lines might be better than being stuck on the other side of the map, but it's not that much better.

If we take Thermopylae as an example, the Spartan forces were high-level units on a very narrow front. Ie, they achieved a high concentration in quantity, and the Persian army could not bring most of their army to the fight at the same time. It also leads me to think that narrow frontages increase the relative value of high-level units.

Concentration also applies to which units to attack. It's generally better to focus on killing off some enemy units than it is to wounding many of them, but leaving them free to continue to act on their turn. At the same time, you usually want to maximise the damage output of your main damage dealers (like mages or high-level units). That also points towards spreading out the high-level units, so they attack first and then low-level units can mop up with their lower damage output.